(1) Field of the Invention
The invention relates to an IC package with an implanted heat-dissipation fin, and more particularly to the IC package whose encapsultant merges a protrusive heat-dissipation fin for rapidly dissipating heat generating by the chip to the ambient.
(2) Description of the Prior Art
The concern of heat dissipation in IC packages or electronic devices is rising to an interesting degree that it just can't be ignored anyway in design; especially for those devices with hi-power chips. Generally in the art, two options are usually applied to resolve the heat-dissipating problem of IC packages; that is, attaching a heat-dissipation fin, or say a heat sink, directly onto the local IC package, or mounting an impinging fan aside the concerned IC package. However, foregoing two resolutions can only form an expediting mechanism that can only remove surface heat of the IC package, not the source heat deep in the poor-heat-conductivity encapsultant of the local IC package. Definitely, though the property of poor heat-conductivity is a nature of the plastic-made (typically, epoxy resin-made) encapsultant, yet the effort to quickly remove the interior heat thereof is still appreciated for the sake of reducing possible breakdown of the chip inside the hot encapsultant.
In the art, various efforts have been utilized to meet the aforesaid heat-dissipation problem to the encapsultant of IC package, and some of them are shown in FIG. 1 through FIG. 5.
Referring to FIG. 1, a drop-in heat spreader is schematically shown in an IC package. A heat-generating chip 11 resting on a pad 12 is shown to be sealed by an encapsultant 10 of the IC package 1. The drop-in heat spreader 13 buried in the encapsultant 10 is located by a predetermined spacing under the pad 12 as well as the chip 11. The drop-in heat spreader 13 is introduced to spread the heat of the chip 11 inside the encapsultant 10. Upon such an arrangement, though the heat generated by the chip 11 can be easily spread out by the drop-in heat spreader 13, yet the heat is obviously still kept inside the encapsultant 10. Furthermore, the location of the heat spreader 13 is adjacent to the PCB side 100 of IC package 1 which in application can only leave a pretty small spacing with the printed circuit board (not shown), and thus the effect of the heat spreader 13 to lead major heat downward to dissipate through the PCB side 100 is definitely not superior.
Referring now to FIG. 2, an IC package 1 with an exposed pad 12 is schematically shown in which a bottom surface of the pad 12 is exposed to, typically flush with, the PCB side 100 of the encapsultant 10. However, as described above, efficiency provided by the heat-dissipation mechanism of the exposed pad 12 to dissipate major heat through the PCB side 100 is not satisfied. Also in the art, the IC package 1 with the exposed pad 12 is usually designed to mount right above a specific metal-skin portion of the PCB (not shown) so that a better thermal way can be established between the PCB and the IC package 1. However, the specific metal-skin portion does make difficult and higher cost to manufacture of the PCB.
Referring now to FIG. 3, the IC package 1 includes an exposed heat slug 13 directly contacting the pad 12 inside the encapsultant 10. Again, such a design still utilizes the downward heat-dissipation path through the PCB side 100 of the encapsultant 10. Except for the manufacturing problem mentioned above, the design of FIG. 3 still has problems in matching accuracy between the pad 12 and the heat slug 13 so that it is seldom used in practice.
In either example shown above, FIG. 1 through FIG. 3, the IC package 1 is one of plastic quad flat packs (known as PQFP) which the manufacturing is critical in molding and thereby the mold-in heat spreader 13 can only arranged at the PCB side 100 of the IC package 1, not the opposing open side 200 which can proved a better ventilation environment after mounting the IC package. On the other hand, for an IC package of ball grid array packs (known as BGA), similar drop-in heat spreader can be also adopted. However, in consideration of the ball grids, the drop-in heat spreader of a BGA IC package is usually arranged close to the open side 200 of the encapsultant 10; i.e. the side away from the printed circuit board or the main board which mounts the IC package.
Referring now to FIG. 4, a BGA IC package 1 having a stacked-die heat spreader 13 is shown. As illustrated, the heat spreader 13 is stacked right on the chip 11 inside the encapsultant 10 so that the major heat-dissipating pathway is directed upward through the open side 200 of the encapsultant 10. However, in this example, the heat spreader 13 is still buried in the encapsultant 10 so that the overall heat-dissipation efficiency promoted by including the heat spreader 13 is obviously not satisfied.
Referring now to FIG. 5, another type of exposed drop-in heat spreader is shown in a BGA IC package. As illustrated, the exposed drop-in heat spreader 13 bridges over the chip 11 in the encapsultant 10 and has both ends foot on the pad 12. Also, the top surface of the heat spreader 13 is exposed to the open side 200 of the IC package 1. By proving the heat spreader 13 of FIG. 5, it is apparent that the heat conducted by the heat spreader 13 can be easily transferred to the atmosphere through the open side 200 of the IC package 1 (precisely, through the top surface of the heat spreader 13). However, the heat generated by the chip 11 can be transferred to the heat spreader 13 only through the poor-conductivity material of the encapsultant 10 between the heat spreader 13 and the chip 11. Definitely, upon such an arrangement, though the difficulty for the heat to dissipate from the IC package 1 to the surroundings is eased, yet the difficulty for the heat to be conveyed out from the chip 11 through the encapsultant's material or the pad 12 still remains. Empirically, the hope of increasing overall heat dissipation of the IC package 1 by including the heat spreader 13 as shown in FIG. 5 is sadly vague.
In the technique shown in FIG. 1 to FIG. 3, heat dissipation of the IC package 1 is mainly interfaced through the heat spreader 13 or the pad 12 at the PCB side 100. On the other hand, heat dissipation of the IC package 1 in FIG. 4 or FIG. 5 is mainly through the heat spreader 13 at the open side 200. No matter whether the packing of the IC package 1 is a BGA or a PQFP, the mold-cavity consideration in molding the packing restricts itself to an encapsultant 10 with a limited volume which just can't accommodate a satisfied heat spreader 13. Also, it is well known in the art that the involvement of any heat spreader 13, described above, in an IC package 1 can only have an enhanced heat dissipation capability by a maximum 20% increase. Therefore, it is usually seen in application that an external heat sink or an impinging fan is introduced to expedite the heat dissipating from the IC package 1 to the surroundings.
Referring now to FIG. 6, an IC package 1 (say the one of FIG. 1) integrates a heat sink 2, or called as a heat-dissipation fin, at the open side 200 of the encapsultant 10 is shown. The heat sink 2 for providing the IC package 1 a broader heat dissipation surface is set onto the open side 200 with a sandwiched adhesive pad 3. Upon such an arrangement, it is clear to see that two heat-transfer retarders exist in this combination to slow down the overall heat dissipation efficiency. One retarder is still the poor-conductivity encapsultant 10, and the other is the adhesive pad 3 which forms substantial contact thermal resistance between the encapsultant 10 and the heat sink 2.
Therefore, it is always appreciated in the art that an improvement to increase the heat dissipation capability of the IC package 1 can be provided.